1. Field of the Invention
This invention relates generally to apparatus for following sun light, and particularly to such apparatus which is used with sun light collecting apparatus arranged to condense sun light and to send condensed sun light to a place where sun light is needed via an optical fiber cable.
2. Description of the Prior Art
Various apparatus for following sun light have been known. In such known apparatus, one apparatus is arranged to sense sun light, one being arranged to perform numerical control through computation of the orbital pass of the sun, one being arranged to move a focal point portion (in the case of a parabolic mirror), and one being arranged to utilize a fixed device which is inclined in a manner of south side down and north side up. On the other hand, as sun light condensing apparatus there is one which condenses sun light using a Fresnel lens by automatically changing its angle to face the sun, thereby sending condensed sun light via an optical fiber cable to a place where sun light is needed. As an example of such an apparatus, there is sun light automatic condensing and transmission apparatus known as "HIMAWARI" produced by La Foret Engineering Co. Ltd. When using a Fresnel lens for condensing sun light, a slight difference in angle of several degrees or less between sun light and the axis of the Fresnel lens results in serious difficulty in sun light condensing. Therefore, apparatus for following sun light of high precision is required. In addition, axis deviation or misalignment may occur due to electrical or mechanical error even though an equatorial movement is controlled in accordance with orbital computation. For such reason, a method which combines sun light sensing and numerical control through orbital computation is generally adopted.
A known sun light sensing apparatus is disclosed in Japanese Patent provisional publication 59-15809. According to a technique disclosed in this publication a casing provided separately from a Fresnel lens is accurately directed to the sun, and a plurality of photosensors are provided within the casing to detect the difference in intensity of light thereby correcting axis deviation.
The above-mentioned conventional apparatus has the following problems since a sun light sensor is located at a place remote from a light-condensing portion where a Fresnel lens and an end plane of incidence of an optical fiber cable are located:
(1) A high precision in mounting the apparatus is required for determining the position and direction of the sun light sensor in accordance with the position and direction of a Fresnel lens.
(2) Diffused light which cannot be used by the sun light condensing apparatus gives undesirable influences to the sun light sensor.